The present invention relates generally to an oxygen content sampling system and more particularly to a sampling system for use in tank vessels of the type for transporting crude oil.
In the early 1970's, inert gas systems ("IGS") became the standard means of protection against explosions and fires in large, crude oil tank vessels. (As used herein, the term "inert" means non-combustible.) An inert gas, such as the stack gas from the tanker boiler, is pumped into the tank, purging combustible oxygen therefrom, and thereby substantially reducing the risk of explosion and/or fire.
Shortly thereafter, an antipollution measure, i.e., crude oil washing ("COW"), was soon developed. Crude oil washing utilizes high pressure jets, pumping crude oil, to wash the tank walls and thereby reduce clingage. Thus, the amount of combustiblecrude oil left on board after unloading is reduced.
Both IGS and COW are now required on crude carriers as a safety and antipollution measures, respectively. These requirements derive from the International Conference on Marine Pollution (1973) and the International Conference on Tanker Safety and Pollution Prevention (1978), often referred to collectively as MARPOL 73/78. Regulations promulgated thereunder are found in the Code of Federal Register, Title 33, Part 157.
To assure vessel safety during crude oil washing, Section 157.164, USE OF INERT GAS SYSTEM, provides, in pertinent part:
"(a) The master of a tank vessel . . . having a COW system . . . shall ensure the following:
(1) Before each cargo tank is crude oil washed, the oxygen content in the tank is measured at each of the following locations in the tank:
(i) One meter from the deck PA2 (ii) In the center of the ullage space."
The oxygen content must be at or below eight percent (8%) of volume to permit crude oil washing.